Imagine a universe without a great filter, where the natural progression of life is to (1) live quietly for a few billion years (2) invent technology for a few hundred years, and (3) expand outwards at close to the speed of light for a few billion years. What sort of aliens would a technologically nascent species expect to see?
I think they would see no aliens at all. The quiet aliens are quiet. The aliens inventing technology are uncommon, just as people aged 37 years 4 days plus or minus 2 seconds are uncommon. The aliens expanding at light speed are invisible until they envelop your planet. If your species evolved naturally on a planet that was not conquered by aliens hundreds of millions of years ago, you’re not going to see any aliens until after you too start expanding out at the speed of light.
I haven’t seen much discussion of the resolution I’ve just outlined. Does anyone know a good counterargument?
ETA Aliens expanding at near light-speed cannot be seen for the same reason that super-sonic jets cannot be heard.
If this very plausible scenario is true then most civilizations at our stage of development would exist when their galaxy was young, because when the galaxy got to be the age of, say, the Milky Way some civilization would have almost certainly taken it over. So under your scenario the Fermi paradox becomes why is our galaxy so old.
This sort of scenario might work if Stage 1 takes a minimum of 12 billion years, so that life has to first evolve slowly in an early solar system, then hop to another solar system by panspermia, then continue to evolve for billions of years more until it reaches multicellularity and intelligence. In that case, almost all civilisations will be emerging about now (give or take a few hundred million years), and we are either the very first to emerge, or others have emerged too far away to have reached us yet. This seems contrived, but gets round the need for a late filter.
It might do, except that the recent astronomical evidence is against that : solar systems with sufficient metallicity to form rocky planets were appearing within a couple of billion years after the Big Bang. See here for a review.
Hmmmm. (ETA: following claim is incorrect) They’re judging that the planets are rocky by measuring their mass, not by noticing that they’re actually rocky.
If you don’t have a Jupiter-sized core out there sucking up all the gas, why would gas planets need to end up as giants? They naturally could do that—that happened with the star, after all, but it doesn’t seem inevitable to me, and it might not even be common.
In that case, the earth-mass planets would be gas planets after all. If you think this is a stretch, keep in mind that these are specifically in systems noted to be low metallicity. Suggesting that they might not be high in metals after all is not much of a stretch.
Actually, Kepler is able to determine both size and mass of planet candidates, using the method of transit photometry.
For further info, I found a non-paywalled copy of Bucchave et al’s Nature paper. Figure 3 plots planet radius against star metallicity, and some of the planets are clearly of Earth-radius or smaller. I very much doubt that it is possible to form gas “giants” of Earth size, and in any case they would have a mass much lower than Earth mass, so would stand out immediately.
Not if evolution of multicellular organisms or complex nervous systems is a random (Poisson) process. That is to say, if the development of the first generation of multicellular life or intelligent life is a random fluke and not a gradual hill that can be optimized toward, then one should not expect behavior analagous to a progress bar. If it takes 12 billion years on average, and 12 billion years go by without such life developing, then such a result is stlil 12 billion years away.
I like it! I also like your gladiatorial solution, but I’m not convinced it would work.
You’re walking through an alleyway and see a $20 bill on the ground. Your forensic skills tell you that it has lain there for 13.2 years, a suspiciously long time. There are several resolutions to this apparent paradox. Perhaps not many people have passed by. Perhaps the bill isn’t really that old. Or perhaps some soft of filter prevents people from picking up the bill (e.g. an economist-eating monster consumes anyone who gets too close).
You take out spray paint and graffiti “I will pick up this $20 dollar bill -->”, thereby extracting yourself from the reference class of people who tried to pick up the $20 and quietly failed. It’s a clever plan, but even if you are the first passerby to think of the plan I don’t believe it advances your interests.
Question, perhaps better for the open thread.
Imagine a universe without a great filter, where the natural progression of life is to (1) live quietly for a few billion years (2) invent technology for a few hundred years, and (3) expand outwards at close to the speed of light for a few billion years. What sort of aliens would a technologically nascent species expect to see?
I think they would see no aliens at all. The quiet aliens are quiet. The aliens inventing technology are uncommon, just as people aged 37 years 4 days plus or minus 2 seconds are uncommon. The aliens expanding at light speed are invisible until they envelop your planet. If your species evolved naturally on a planet that was not conquered by aliens hundreds of millions of years ago, you’re not going to see any aliens until after you too start expanding out at the speed of light.
I haven’t seen much discussion of the resolution I’ve just outlined. Does anyone know a good counterargument?
ETA Aliens expanding at near light-speed cannot be seen for the same reason that super-sonic jets cannot be heard.
If this very plausible scenario is true then most civilizations at our stage of development would exist when their galaxy was young, because when the galaxy got to be the age of, say, the Milky Way some civilization would have almost certainly taken it over. So under your scenario the Fermi paradox becomes why is our galaxy so old.
Or why stage 1 is so long.
This sort of scenario might work if Stage 1 takes a minimum of 12 billion years, so that life has to first evolve slowly in an early solar system, then hop to another solar system by panspermia, then continue to evolve for billions of years more until it reaches multicellularity and intelligence. In that case, almost all civilisations will be emerging about now (give or take a few hundred million years), and we are either the very first to emerge, or others have emerged too far away to have reached us yet. This seems contrived, but gets round the need for a late filter.
I don’t get the reason panspermia needs to be involved. Simply having a minimum metallicity threshold for getting started would do the job.
It might do, except that the recent astronomical evidence is against that : solar systems with sufficient metallicity to form rocky planets were appearing within a couple of billion years after the Big Bang. See here for a review.
Hmmmm. (ETA: following claim is incorrect) They’re judging that the planets are rocky by measuring their mass, not by noticing that they’re actually rocky.
If you don’t have a Jupiter-sized core out there sucking up all the gas, why would gas planets need to end up as giants? They naturally could do that—that happened with the star, after all, but it doesn’t seem inevitable to me, and it might not even be common.
In that case, the earth-mass planets would be gas planets after all. If you think this is a stretch, keep in mind that these are specifically in systems noted to be low metallicity. Suggesting that they might not be high in metals after all is not much of a stretch.
Actually, Kepler is able to determine both size and mass of planet candidates, using the method of transit photometry.
For further info, I found a non-paywalled copy of Bucchave et al’s Nature paper. Figure 3 plots planet radius against star metallicity, and some of the planets are clearly of Earth-radius or smaller. I very much doubt that it is possible to form gas “giants” of Earth size, and in any case they would have a mass much lower than Earth mass, so would stand out immediately.
I forgot about photometry.
Not if evolution of multicellular organisms or complex nervous systems is a random (Poisson) process. That is to say, if the development of the first generation of multicellular life or intelligent life is a random fluke and not a gradual hill that can be optimized toward, then one should not expect behavior analagous to a progress bar. If it takes 12 billion years on average, and 12 billion years go by without such life developing, then such a result is stlil 12 billion years away.
I like it! I also like your gladiatorial solution, but I’m not convinced it would work.
You’re walking through an alleyway and see a $20 bill on the ground. Your forensic skills tell you that it has lain there for 13.2 years, a suspiciously long time. There are several resolutions to this apparent paradox. Perhaps not many people have passed by. Perhaps the bill isn’t really that old. Or perhaps some soft of filter prevents people from picking up the bill (e.g. an economist-eating monster consumes anyone who gets too close).
You take out spray paint and graffiti “I will pick up this $20 dollar bill -->”, thereby extracting yourself from the reference class of people who tried to pick up the $20 and quietly failed. It’s a clever plan, but even if you are the first passerby to think of the plan I don’t believe it advances your interests.